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Файл:Materials Processing Technology Part 2. Coursebook
.pdf
Unit 3
typically as a powder, sometimes as a liquid, suspension or
wire
feedstock type plasma gas composition flow rate energy
input
Plasma Spraying
Plasma spraying is a coating process in which powders of the coating
materials are fed into the plasma jet at around 10 000 K, at which the coating
materials melt and are sprayed over the substrate to be coated.
Plasma Spray Processing is a method of giving a material a protective
coating through the form of a plasma spray.
A plasma is an electrically conductive gas which contains charged
particles. When gases reach a high excited state, they can lose some of their
electrons and become ionized which produces a plasma that is electrically
charged with ions and electrons. In this plasma there are four gases, which are
involved with the process:
-Hydrogen
- Helium
- Argon
- Nitrogen.
Plasma-spraying is a feasible way to coat metallic substrates with glass
powders.
The advantages of the plasma-sprayed technique are in creating reasonably high
coating bond strength and mechanical properties
The theory behind this process is called "Plasma Jet Theory" or "Plasma
Flame Theory" even though there is no flame involved in the process.
Plasma spraying is a thermal spray process in which
- a molten or heat softened material is sprayed onto a surface to create a coating;
- a powder is injected at a high temperature plasma flame;
- this material is then heated rapidly and accelerated to a very high velocity;
- the hot material hits the surfaces and cools very quickly to form a coating.
The completed process can be called a "cold process" because the temperature of
the object being coated can be kept very low, which avoids damage during
processing, metallurgical effects and distortion.
The material deposited in plasma spraying process (feedstock):
The technological parameters that influence the interaction of the particles
with the plasma jet and the substrate:
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torch offset distance substrate cooling
lower strength modulus higher strain tolerance lower thermal
conductivity
lower electrical conductivity rapid solidification metastable
phases
√ to produce coatings on structural materials;
√ to produce free-standing parts in the form of plates, tubes,
shells, etc.;
√ for powder processing (spheroidization, homogenization,
modification
of chemistry, etc.);
√ to create porous structures, suitable for bone ingrowth, as a
coating
for medical implants;
√ to modify the surface chemistry of polymers, etc.
Deposit properties:
Young's modulus or Young modulus is a mechanical property that measures
the stiffness of a solid material. Young's modulus is named after the 19th-century
British scientist Thomas Young.
Strain is a measure of deformation representing the displacement between
particles in the body relative to a reference length.
Applications:
READING Plasma spraying
→ Read Study Skill
___1 Read the texts from Unit 3 of the Textbook.
___2 Survey the texts from Sections 9.1 to Section 9.3 and underline the
information which answers the questions.
1) What kind of gas is termed plasma?
2) What is the history of machining by plasma?
3) What is the system of plasma machining?
4) Which factors provide great efficiency of the plasma arc system?
5) What types of materials are tackled by the plasma jet system?
6) What types of shielding gases are used for assisting purposes when machining
different materials?
32
7) In which case the shielded gas is replaced by water?
the plasma jet the nozzle the plasma torch argon copper
molten
ultra-violet light a continuous arc consumable metal wires
ionized gas
8) What is the main drawback in using compressed air in plasma machining?
______3 Survey the texts from Sections 9.4 to Section 9.5 and underline the
information which answers the questions.
1) What type of gas is used to create the heat source in the plasma spraying
process?
2) What is the purpose of adding hydrogen as a secondary gas to the plasma gas
stream?
3) What are the three stages of the plasma spraying process and the factors
affecting plasma spraying performance?
4) What are the benefits in using thermal spraying technology?
5) What is the structure of a thermal spray system?
6) Which technological parameters influence the deposit properties in the
plasma spraying process?
7) Which methods are used to stabilize the plasma spraying systems?
8) What are the basic characteristics of modern vacuum plasma spraying
technology?
9) Which features distinguish the cold spraying technology?
VOCABULARY DEVELOPMENT
___1 Study Section 9. Match the following words and phrases with their
definitions
and characteristics.
____1 Complete the following sentences with the words from the box.
1) In plasma machining __________ is generated between a hot tungsten
cathode and the water-cooled copper anode.
2) The double arcing effect between ________ and the workpiece damages the
electrode and the workpiece.
3) Only __________ is emitted as a jet causing temperature as high as 16,600 ºC.
4) Water forms a radial jacket around __________.
33
5) Electrically conductive materials, such as stainless and chrome nickel alloy
STUDY SKILL Using a dictionary: effective or efficient?
Use an English-English dictionary to read the definitions and look at
the example sentences to use the words correctly:
a) producing the result → effective
that was wanted or
intended
b) working well, without → efficient
wasting time, money,
or energy
effective:
There are many effective ways of using videos in language teaching.
/
Our training programmes cover a range of effective management
techniques. /
the most effective ways of reducing inner city congestion
efficient:
The company is well-known for its friendly, efficient service. /
The first thing the company did was to create an efficient and
accurate filing system. / Lighting is now more energy efficient.
steels, aluminum, and ________ can be machined by air plasma.
6) The most common gas used to create the plasma is ________.
7) The required coating material is introduced into the heat source, the material is
melted and becomes __________.
8) In plasma spraying process, the material to be deposited is introduced into
__________, emanating from a plasma torch.
9) Electric arc spraying produces ____________, which may damage delicate
body tissues.
10) Wire arc spray is a form of thermal spraying where two ___________ are
fed independently into the spray gun.
_____ 2 The link below will help you use Quizlet to enrich your vocabulary
on the topic
The Plasma Spraying Process:
https://quizlet.com/392333719/plasma-spraying-and-other-forms-of-sprayingflash-cards/?new
34
COLLOCATIONS
improve/increase efficiency: The company is taking steps to
improve efficiency and reduce costs.
promote efficiency (= develop or encourage efficient ways of doing
something)
greater/increased efficiency: In a search for greater efficiency, the
two departments have merged.
maximum efficiency: The boat’s design helps it to move with
maximum efficiency.
energy efficiency: Energy efficiency can play a huge role in
reducing pollution.
fuel efficiency: Better fuel efficiency can be achieved by driving
more slowly.
(from Dictionary of Contemporary English for Advanced
Learners,
Longman 2009)
______3 Choose the correct word in bold ‘effective’ or ‘efficient’.
1) The project looks at how we could be more effective / efficient in encouraging
students to enter teacher training.
2) Simple antibiotics are efficient / effective against this organism.
3) They have had effective / efficient control of the area since the security forces
left.
4) The electrical discharge machining process is most widely used to produce
complicated shapes, such as turbine blades. It is also efficient / effective as a
deburring process.
5) Computer-integrated manufacturing can free electrical discharge machining
from its island of automation, achieving more efficient / effective and costeffective production.
6) while most holes are drilled with a single laser pulse of high energy, it is more
effective / efficient to drill deep holes with multiple pulses of low energy.
7) As the entrance angle of the laser beam with respect to the surface becomes
smaller, the effective / efficient surface power density is reduced.
8) An electron beam deflection coil is able to scan the electron beam a distance of
0,1 mm in 1 ms, meaning that efficient / effective tracking can be accomplished
with work piece motion as fast as 100 mm/s.
35
9) Computer numerical control lathes are particularly efficient / effective for
STUDY SKILL Using a dictionary: impact or influence?
The dictionary entries will help you use the words.
a) the effect or influence → impact
that an event, situation
has on someone or something
b) the power to affect the way → influence
someone or something develops,
behaves, or thinks without using
direct force or orders
impact:
We need to assess the impact on climate change. / Higher
mortgage rates have already had a major impact on spending. /
The computer has made a great impact on modern life.
influence:
As a scientist, his influence was immense. / the union’s influence
over local politics / The stars’ influence on people’s lives has not
been proved.
COLLOCATIONS
have an influence on sb/sth
a big/great influence
an important/significant/major influence
considerable influence
a growing influence
a direct/indirect influence
(from Dictionary of Contemporary English for Advanced
Learners,
Longman 2009 )
complicated programs to make parts that would be more difficult to make on
manual lathes.
10) Robots are more efficient /effective than human beings because they are so
precise.
11) Thermal imaging is a fast, cost efficient / effective way to perform detailed
thermal analysis.
12) Our efficient/ effective new machines are much cheaper to run.
36
_____4 Choose the correct word in bold ‘impact’ or ‘influence’.
STUDY SKILL Modals
The modals in English include the auxiliary verbs and their various
paraphrases.
Scientific writing uses these words in more restricted ways than
general English. They are most frequently used to indicate 1)
obligation, 2) probability, 3) capability.
Modals of Obligation
Scientific writing is more concerned with the correct way of doing
something, and less with moral obligation. The modals that express
obligation (may, should, must and shall) may be ranked according to
the degree of choice that the human subject (implied or stated) has.
1) They expect the meeting to have a market influence/impact on the future of
the country.
2) Van Gogh had a major influence/ impact on the development of modern
painting.
3) The government should continue to use its influence / impact for the release of
all hostages.
4) Despite the high investment cost of laser welding equipment, it is expected
that laser welding will have a great impact /influence on fabrication and
manufacturing industries.
5) In case of hard and brittle materials such as glass, the machining rate is high
and the role played by free influence/ impact can also be noticed.
6) The cost reduction and good environmental impact /influence make the ice jet
machining even better.
7) The environmental influence/ impact of machining processes is becoming
increasingly significant in view of new legislation in the 1990s.
8) Upon impact / influence, the kinetic energy6 of the electrons is converted into
the heat necessary for the rapid melting and vaporization of any material.
9) An unexpected shutdown of even a minor piece of equipment could have a
major influence/ impact on production.
10) Darwin’s ideas have had a profound impact / influence on our view of the
world.
11) The full impact / influence of changes in computer technology will be felt
within the next few years.
37
may*
should
must
shall
The compressor system may be
insulated.
The compressor system should be
insulated.
The compressor system must be
insulated.
The compressor system shall be
insulated.
*In scientific English, may occurs most frequently.
Textbooks frequently use may with a passive verb to describe
legitimate operations.
The amount of cholesterol may be determined from a blood sample.
The pressure may be calculated by means of the formula P=T/V.
The modal shall is used by convention in building codes and
design specifications, indicating that the instructions must be
followed exactly.
The condensers shall be adequately sized to operate satisfactorily
from 50 ºF to 110 ºF ambient temperature.
The critical speed of the fan wheel shall not be less than 25 %
above the maximum specified speed.
Modal
Past modal
Paraphrase
may
should
must
shall
may have
should have
had to
had to
(has the option)
is recommended
is required
is required
_____5 Add the appropriate modal of obligation (may, should, must, shall)
to the blanks.
1) Researchers conclude that gas stoves ____________ be used without adequate
ventilation.
2) Cold box temperatures in the specified refrigeration unit ___________ be
between - 40º and - 80 ºF.
3) Metallic sodium ____________ be allowed to come into contact with water;
otherwise, it will react violently.
38
4) All specified ductwork exposed to weather ___________ be insulated with 3-
STUDY SKILL Modals (2)
Modals of Probability
Probability expresses the degree of certainty that something is
correct.
The modals that show probability are must, should, may and
might or could, ranging from relative certainty to relative
uncertainty. They frequently occur in conclusions and abstracts
where the implications of results are discussed.
Modal
Past modal
Modal paraphrase
must
should
may
might/
could
must have
should have
may have
might have /
could have
is certain
is likely
is/will perhaps
is/will possibly
inch thick insulation and __________ be weather proofed.
5) The contrast at any point on the screen ___________ be defined as the ratio of
the fractional charge in illumination to the general illumination.
6) It __________ be noted that the deflection of the light ray is a measure of the
average density gradient integrated over the X coordinate.
7) Vertical bracing ___________ be so arranged that the entire width of all
walkway areas have a minimum clear vertical opening of 7 feet.
______ 6 Add the appropriate modal of probability (must, should, may,
might/could) to the blanks.
1) New methods of breaking the bonds of hydrocarbons such as petroleum
_________ allow the manipulation of the chemicals into drugs and similarly
complex materials.
2) Fleming realized that the bacteria in the petri dish ___________ killed by the
penicillin molds nearby.
3) New data suggest that even a modest nuclear war ____________ have
devastating effects on the atmosphere and global climate.
39
4) If the absorption spectrum of a star includes the absorption spectrum of
STUDY SKILL Modals (3)
Modals of Capability
Capability expresses the degree of ability that something or
somebody has.
The modals that show capability are can, could (hypothetical
ability),
should be able to, may be able to, and might be able to, ranging
from strong capability to weak capability.
Modal
Past modal
Modal paraphrase
+V
ing
can
could
should be able
to
may be able to
might be able
to
could
could have
should have been
able to
may have been able
to
might have been able
to
is capable of
would be capable of
should be capable of
may be capable of
might be capable of
Can occurs most frequently in scientific English compared to
the other modals of capability.
hydrogen, that star _________ contain hydrogen.
5) When scattered cumulus clouds are present between 3,000 and 10,000 feet
above the earth, the ensuing weather __________ be fair.
6) New research suggested that asbestos _________ be mutagenic itself, but
rather an enhancer of other carcinogens.
_______7 Add the appropriate modal of capability (can, could, should be
able to, may/might be able to) to the blanks.
1) Spontaneous electrical firing ______________ occur anywhere in the heart
under certain conditions.
2) If no sterilizer were available, medical instruments _______________ be
sterilized by chemical means.
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